Amyloid senile plaques (SPs) and neurofibrillary tangles (NFTs) are neuropathological hallmarks of Alzheimer's disease (AD) that also accumulate in key brain regions in association with normal aging. Our group has synthesized a small molecule probe, 2-(1-{6-[(2-[F-18]Fluoroethyl)(methyl)amino]-2-naphthyl}ethylidene)malononitrile ([18F]FDDNP), which provides excellent visualizations of NFTs, SPs, and diffuse amyloid in AD brain specimens using fluorescent microscopy, and in vivo human positron emission tomography (PET) studies show that [18F]FDDNP labels medial temporal cortex in AD patients. This program project grant is designed to determine whether this method of plaque and tangle PET imaging (1) correlates with the expected accumulation of neuropathological changes associated with aging and dementia (AD and frontotemporal dementia [FTD]);(2) predicts future decline in people at risk for AD and in patients with dementia;and (3) augments other informative imaging (e.g., structural and functional magnetic resonance imaging [MRI], FDG-PET measures of glucose metabolism, [18FJMPPF-PET measures of serotonin receptor density), neuropsychological, and genetic risk (apolipoprotein E-4 [APOE-4], H1 haplotype of the tau gene) measures in diagnosis and differential diagnosis of normal aging and dementia. An Administrative and Clinical Core, a Chemistry and PET Imaging Core, and an Image Analysis Core will support three proposed projects: (1) Visualizing brain A-beta, tau and serotonin receptor densities;(2) Clinical plaque and tangle imaging in aging and dementia;and (3) Multi-modal brain imaging in aging and dementia. This infrastructure will provide an opportunity to study transgenic animal models, neuropathological correlations, binding characteristics, and longitudinal PET, MRI, neuropsychological and genetic risk data in patients with AD and frontotemporal dementia, people with MCI, and younger and older adult controls. This project will expand an established program in early detection and prevention of AD, designed (1) to identify presymptomatic persons most likely to benefit from early intervention and (2) to provide an objective, noninvasive means to monitor therapeutic trials.